1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus that is capable of forming an image on a recording material (i.e., a recording medium), such as a sheet. More specifically, the present invention relates to an image forming apparatus, such as a copying machine or a printer.
2. Description of the Related Art
In an image forming apparatus using electrophotographic image forming processes, a method for notifying or estimating the amount of a developer remaining in a developing device is conventionally disclosed.
As discussed in Japanese Patent Application Laid-Open No. 5-6092, as a method for directly detecting the amount of a developer, it is conventionally known to detect an electrostatic capacity amount that is variable depending on the amount of a developer remaining in a developing device and calculate the residual developer amount based on the detected electrostatic capacity amount. Further, as discussed in U.S. Pat. No. 5,649,264, a combination of an infrared light-emitting diode (LED) and a light-receiving sensor is usable to detect the amount of a remaining developer.
Further, as a method for indirectly estimating the amount of a developer, as discussed in Japanese Patent Application Laid-Open No. 2001-318566, it is conventionally known that a developer consumption rate can be estimated based on image information (e.g., pixel count value) in an image forming operation and the remaining amount detection can be performed based on the estimation result.
Further, as a representative configuration of the electrophotographic image forming apparatus capable of simplifying the replenishment of the developer or the maintenance of the developing device, it is conventionally known that the developing device can be configured as a “developing cartridge” that is detachable from the main body of the image forming apparatus. Further, it is conventionally known that the developing device can be integrally formed with a photosensitive member and other process units as a “process cartridge” that is detachable from the main body of the image forming apparatus.
Further, as another configuration of the electrophotographic image forming apparatus capable of simplifying the replenishment of the developer or the maintenance of the developing device, it is conventionally known that the developing device can be configured as a “developing process cartridge” that is detachable from the main body of the image forming apparatus. Further, it is conventionally known that the developing device can be integrally formed with a photosensitive member and other process units as a “process cartridge” that is detachable from the main body of the image forming apparatus.
Further, it is conventionally known to provide a notification unit (e.g., a display unit) in the above-described developing process cartridge to measure the remaining developer amount (i.e., the residual developer amount) in a developer container and warns about a coming shortage of the residual developer. Further, the notification unit (e.g., the display unit) can be used to notify a user of a usage limit of the developing cartridge and encourage the user to exchange developing cartridges.
In this case, a control device sets an appropriate warning level to generate warning in a state where a certain amount of developer still remains in a developer container and encourage a user to exchange developing cartridges. The reason why the above-described warning setting is required is because, for example, an image defective may occur because of the presence of a developer deviating along the longitudinal direction of a developer carrier (e.g., a developing roller) if the developer is used continuously until the developer container becomes empty.
However, the following problems will arise if the notification unit (e.g., the display unit) is configured to display a warning message (or indication) when the remaining developer amount reaches a predetermined threshold level. More specifically, if the image forming apparatus performs formation of images at lower print rates, the image defective may occur at early timing before the remaining developer amount reaches the threshold level (i.e., in a state where a relatively larger amount of developer remains and the warning is not yet required). More specifically, it is generally believed that the deterioration degree of the developer stored in a developer storage container is relatively higher if the print rate is lower compared to the deterioration degree in a case where the print rate is higher.
For example, the relationship between the print rate and the deterioration of the developer will be described below. The developer includes resin particles containing pigment (as base material) and external additives (such as lubricant and charge control agent). The developer can obtain a desired amount of electric charge when the developer is rubbed by a developing blade on the developer carrier.
However, the external additives may be embedded between the resin particles when the developer is rubbed by the developing blade to obtain the desired amount of electric charge.
If the external additives are completely embedded between the resin particles, the developer cannot obtain the desired amount of electric charge any more. This phenomenon is generally referred to as the “deterioration of the developer.” The deteriorated developer possibly causes an image defective because the obtainable charge amount is insufficient.
If the developer obtains the desired charge amount by the developing blade, the developer is conveyed to a predetermined position of a developing portion where an image carrier is brought into a confronting relationship with the developer carrier in such a way as to develop an electrostatic latent image. On the other hand, if the developer has not been used in the development of an electrostatic latent image, the developer is conveyed into the developer storage container.
The developer, if it has not been used in the development of an electrostatic latent image and returned to the developer storage container, is already in a deteriorated state because the developer has been rubbed sufficiently by the developing blade. Therefore, when the image forming apparatus performs formation of images at lower print rates, the percentage of the developer not having been used in the development of an electrostatic latent image increases. As a result, the percentage of the deteriorated developer returned to the developer storage container portion increases.
Accordingly, the entire deterioration degree of the developer existing in the developer storage container becomes higher when the image forming apparatus prints a greater number of images at lower print rates, compared to a case where the image formation is performed at higher print rates.
From the foregoing description, it is generally believed that the image defective possibly occurs at early timing before the remaining developer amount reaches a predetermined threshold level if the image forming apparatus prints many images at lower print rates.